During the past year, there have been two areas of research ongoing in the Molecular Immunology Section: 1) identification of structure/function relationships of human CD8+ T cell antigen-specific receptors (TCR) and 2) determination of differential gene expression in CNS lesions of MS patients. Structural analysis of TCR recognition has been examined using T cell assays, kinetic and thermodynamic binding assays, and X-ray crystallography. The emphasis on these studies has been on the mechanism of how TCRs that are specific for multiple peptides presented by HLA-A2 actually bind to the HLA-A2 molecule. The overall conclusion is that there are conserved amino acids on the alpha one (K66) and alpha two (Q155) helices of the HLA-A2 molecule that are key anchor residues that are recognized by most HLA-A2-restricted TCRs. For most HLA-A2/peptide complexes whose structures have been solved, the side chains of these key amino acids also contact the bound peptide. These findings demonstrate that the molcular mechanism underlying MHC restriction is that the TCR/MHC interaction cannot be physically separated from the peptide/MHC interaction because key elements of the MHC molecule not only are directly contacted by the TCR but these same MHC elements also contribute to the conformation of the bound peptide. Analysis of differential gene overexpression in CNS lesions of MS patients and the brains of mice with EAE by cDNA microarray technology has been performed by monitoring the expression pattern of over 2800 genes known or suspected to be involved in immune responses. Four genes were found to be overexpressed in each of 18 MS lesions examined and in the brains of two strains of mice with EAE compared to normal white mattter. The product of one of these genes, 5-Lipoxygenase (5-LO), was found in the lesions of four different MS patients but not in normal white matter by immunohistochemistry. Since 5-LO is the enzyme crucial for the biosynthesis of inflammatory leukotrienes, this previously unreported proinflammatory enzyme in MS lesions may contribute to pathology, and provide a new opportunity for therapeutic intervention. Thus, cDNA microarray technology represents a powerful new tool for the identification of genes not previously associated with the MS disease process.